The FBI has devoted “considerable resources” to fixing problems with its handling of National Security Letters, and has made definite progress, a Justice Department audit finds.

Intriguingly, the audit also finds the FBI’s use of the investigative tool has jumped to levels exceeding those found during some years of the Bush administration.

In an extensive follow-up to past audits, the Justice Department’s Office of Inspector General noted that officials have “implemented 23 of 28 recommendations” that include “creating new internal controls, providing guidance and training to FBI personnel (and) establishing new record-keeping practices.”

National Security Letters are written directives ordering third parties such as telephone companies, Internet service providers and financial institutions to turn over information. Past audits found “repeated instances of FBI misuse” of these letters, auditors noted.

The new audit includes fresh information on the letters’ use, though the auditors also noted that the FBI insisted on redacting some details that the auditors felt should be made public.

In 2008, the last year of the Bush administration, the report notes that the FBI requested 41,299 National Security Letters. In 2009, the first year of the Obama administration, the number of requests fell to 30,442.

But in 2010, the number of requests jumped back up to 54,935, more than in all but one year of the Bush administration. In 2011, the last year for which records are made public, the FBI requested 46,648 letters.

“According to the FBI, the number of NSLs issued in any given year is a function of the needs of the national security investigations conducted in that year,” the audit reported.

A “majority” of the requests are “in furtherance of counterterrorism investigations,” the audit notes.

Though details are blacked out from the publicly released version, the audit reports that “requests for telephone subscriber information comprised the largest percentage” of requests.

FBI officials, in their formal response to the audit, said they were “pleased” with the observations about improvements and declared officials “will work to bring closure” to the remaining recommendations.